The Methanol to Olefin (MTO) process is successfully commercialized by UOP. This process is covered by many UOP patents. New improvements in the catalyst compositions and process schemes are being made to improve the overall economics of the process. Flexibility in the MTO product selection to integrate the MTO plant within the existing petrochemical infrastructure is a challenge while designing new plants. The MTO process produce significant amount of C4 olefins, C5 olefins, aromatics and heavier species in addition to ethylene and propylene which are the desirable products. The effective utilization of these by-products can significantly improve the economics of the process.
The U.S. Pat. No. 6,303,839 issued to UOP explains an integrated MTO-Olefin cracking process. The oxygenate feed stock is catalytically converted to paraffin's, light olefins (ethylene, propylene) and heavier olefins using a silicoaluminophosphate (SAPO) molecular sieve catalyst in the vapor phase. The product is separated and the mixed butenes and heavier olefins are reacted in a second reactor to produce additional propylene. The catalyst used in the second reactor is same as that in the MTO reactor.
The U.S. Pat. No. 7,317,133 issued to UOP explains a process for enhanced olefin production. In this process, the MTO reactor product is separated in to light olefins and heavier olefins. The heavier olefins are further separated in a second stage separation to produce a C4 to C7 olefin stream and a heavier stream. The C4 to C7 olefin stream is then passed through an olefin cracking reactor (OCP) to convert a portion of the olefins to light olefins like ethylene and propylene. The catalyst in the OCP reactor is from a family of crystalline silicate of MFI or MEL like ZSM-5 or ZSM-11.
While there are many similar patents that cover integrated MTO-OCP process to maximize ethylene and propylene, none of these processes has flexibility to control the Propylene to Ethylene (P/E) product ratio. The P/E product ratio is largely determined by the MTO and OCP reactor yields. A high P/E ratio, preferably more than 3 is desirable due to the increased demand for propylene.